feat: added is_closed method to connection class

[NI1993]

Description

Motivation and Context

Testing

Screenshots (if appropriate)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Checklist

• Local run of ./build.sh succeeds
• Code changes have been run against the repository's pre-commit hooks
• Commit messages follow Conventional Commit Specification
• I have read the README document
• I have added tests to cover my changes
• I have run all unit tests using pytest test/unit and they are passing.

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